1. Field of the Invention
The present invention relates to a pattern forming method, an electronic device manufacturing method and to an electronic device. More specifically, the present invention relates to a method of forming a randomly arranged hole pattern having minute, isolated hole pattern, a method of manufacturing an electronic device and to the electronic device.
2. Description of the Background Art
Formation of a hole pattern by photolithography requires, different from a line pattern, local presence of electromagnetic field when viewed two dimensionally. Therefore, miniaturization is difficult in principle. Further, when a pattern of holes is formed by a positive photo-resist, effective image contrast inherently becomes smaller.
Particularly, formation of a minute, isolated hole with high process margin is difficult, as effective super-resolution technique has not been known. Therefore, formation of a minute, isolated hole remains one factor hindering device miniaturization.
Because of the above-described limitation in principle, an optical image formed by a pattern of regularly arranged holes has image quality inferior to that of a pattern of dense lines that is a one-dimensional pattern. For such a hole pattern, however, super-resolution technique represented by modified illumination method is available. Therefore, by applying a high-resolution photo-resist having superior separation performance, minute holes of high density can be formed with high process margin.
In contrast, when a dark point image is formed, excellent image quality of a pattern of random arrangement can be attained by applying a phase-cancellation image using a phase shift mask under optimally modified illumination, as disclosed by the inventors of the present invention (see References 1 and 2 below).
Reference 1: Japanese Patent Laying-Open No. 2004-251969
Reference 2: S. Nakao et al., “Zero MEF Hole Formation with Atten-PSM and Modified Illumination”, Proc. of SPIE Vol. 5040 (2003), pp. 1258-1269
Conventional formation of a pattern of randomly arranged holes by applying a phase-inverted image using the phase shift mask requires a negative photo-resist, as described above. For the state-of-the-art ArF excimer laser exposure, however, there is no negative photo-resist of excellent performance. Therefore, it has been difficult by the conventional method to realize characteristics sufficient for practical use with the wavelength of ArF excimer laser.